The amount of pollutants and waste generated by industrial facilities has become an increasingly costly problem for manufacturers and a significant stress on the environment. Companies, therefore, are looking for ways to reduce pollution at the source as a way of avoiding costly treatment and reducing environmental liability and compliance costs.
The United States Agency for International Development (USAID) is sponsoring the Environmental Pollution Prevention Project (EP3) to establish sustainable programs in developing countries, transfer urban and industrial pollution prevention expertise and information, and support efforts to improve environmental quality. These objectives are achieved through technical assistance to industry and urban institutions, development and delivery of training and outreach programs, and operation of an information clearinghouse.
EP3 pollution prevention diagnostic assessments consist of three phases: pre-assessment, assessment, and post-assessment. During pre-assessment, EP3 in-country representatives determine a facility's suitability for a pollution prevention assessment, sign memoranda of agreement with each facility selected, and collect preliminary data. During assessment, a team comprised of U.S. and in-country experts in both pollution prevention and the facility's industrial processes gathers more detailed information on the sources of pollution, and identifies and analyzes opportunities for reducing this pollution. Finally, the team prepares a report for the facility's management detailing its findings and recommendations (including cost savings, implementation costs, and payback times). During post-assessment, the EP3 in-country representative works with the facility to implement the actions recommended in the report.
This assessment evaluated a dye house serving a variety of fabric manufacturers. The objective of the assessment was to identify actions that would:
Overall, the assessment identified eleven pollution prevention pollution opportunities that could reduce energy use at this facility and avoid the release of 0.5 metric tons of air emissions each year. Water use could be reduced by nearly 70,000 cubic meters per year, and chemical releases to surface waters could also be reduced. Two of the opportunities - recycling bleach rinse water and capturing the heat in boiler blowdown water - reduced annual operating costs by about $9,000 for an initial investment of $1,700.
This facility is a dye house serving fabric manufacturers. The facility operates two twelve-hour shifts, six days per week. In 1992, the facility wet-processed 960,000 kg of fabric, consisting primarily of cotton-synthetic blends.
Fabric dyeing at this facility involves a number of steps that must be carried out in proper sequence and under optimal conditions. The process consists of filling tanks containing fabrics with water, and sequentially:
EP3 is sponsored by the U.S. Agency for International Development.
At the time of the assessment, there were a number of pollution problems at the facility, including:
The assessment identified eleven pollution prevention opportunities that could address the problems identified, with significant environmental and economic benefits to the facility. Table 1 lists the opportunities recommended for the facility, and presents the environmental benefits, savings and implementation costs for each. Many of the recommendations can be implemented with no capital investment. Further, many can be implemented immediately, and most are not dependent upon other projects for their initiation. The recommendations can be grouped into four general categories:
| Unit Operation | Pollution Prevention Opportunity | Environmental Benefit and Cost Savings | Capital Cost to Implement |
|---|---|---|---|
| Bleach Rinsing | Reduce water use, recover process chemicals and heat by recycling bleach rinse water. | Reduce water use by 23,000 cubic meters per year. Reduce water costs by $6,300 per year. | $1,200 to replumb tanks |
| Dye Rinsing | Reduce water use by recycling second dye rinse. | Reduce water use by 43,000 cubic meters per year. Reduce water costs by $12,800 per year. | $2,400 for two tanks and plumbing. |
| Boiler | Recover heat from boiler blowdown. | Reduce fuel used by $2,700 per year, reduce temperature of effluent. | 500 |
| Dye Process | Reduce liquor ratio in jet dyeing. | Reduce water use by up to 4,800 cubic meters per year. Reduce water costs by $1,300 per year. | None |
| Chinese Reactive Dyes | Control dye process using Fong equipment. | Reduce redye and chemical costs (unquantified). | None |
| Dye Process | Use Fong equipment to determine acetic and formic acid concentrations for specific dyes. | Reduce use of chemicals, reduce BOD 5 of effluent (unquantified). | None |
| Reactive Dyes | Determine actual price break point for one and two-step dyeing. | Reduce dye use, decrease cost of dyeing (unquantified). | None |
| Dispersed Red 60 Dye | Change dyes to improve heat fastness. | Reduce dye in effluent, reduce dye costs (unquantified). | None |
| Effluent | Reduce suspended solids in effluent by installing screens. | Keep effluent in compliance. | 120 |
| Effluent | Reduce sulfide in effluent by aeration and exposure to light. | Reduce sulfide in effluent, prevent sewer deterioration. | 120 |
| Effluent | Determine effluent concentrations for controlled parameters, determine reduction priorities. | Keep effluent in compliance, identify priority pollutants for reduction. | $600 for testing |
| TOTALS: | $9,000 to $23,000 annually, plus unquantified opportunities. | $2,500 to $5,000 | |
Water use at the facility is now near the limits of system capacity. The resulting low water pressure increases the cycle time for fabric processing by extending the time needed to fill jets with water. Any reduction in water use would therefore increase productivity as well as reduce water purchase costs. If large quantities of the same colored fabric are dyed in succession, countercurrent rinsing can be built into the structure of jet dyeing equipment. This would reduce water use, while maintaining the same quality of final product.
Bleach rinsing involves two successive overflowing rinses. Recycling the second bleach rinse back into the process for use in the first rinse could begin immediately to reduce water use, water reuse is standard practice on large through-put machinery. Assuming that half of the 8,200 liters used for the two bleach rinses is reused and that 5,680 loads per year are processed, the quantity of water that could be saved is 23,300 cubic meters per year, saving over $6,400. If rinse processes are modified to use recycled second rinse water, the additional savings would be 43,300 cubic meters per year worth $12,800, for a total savings of nearly 70,000 cubic meters per year worth almost $20,000. If water from both rinses is recycled, total water use could be reduced by about 25 percent.
Currently, after polyester dyeing, the solution in the jet is cooled with a heat exchanger from 130C to 80C. By retrofitting the boilers with a continuous blowdown system, and routing the water from that system through the heat exchange coils in the two steel tanks, heat could be recovered into the used jet cooling water. Water for both fabric processing and boiler feed could be drawn from this tank, which would make maximum use of the heat from both jet cooling and boiler blowdown water. The savings would be about $2,700, assuming a 50 percent efficient heat transfer mechanism. Reusing rinse waters and capturing heat from the boiler blowdown also reduces the temperature of effluent. This is significant because effluent has sometimes exceeded 75C, when the standard is 35C.
Jet dyeing equipment of the type used at the facility could be run at lower liquor ratios than the current 10:1, perhaps as low as 5:1. Reducing the liquor ratio to 5:1 would save 4,800 cubic meters of water per year, worth over $1,300. Additional unquantified savings might be gained through better dye utilization. In addition, the facility could use a dye process simulator to realize significant savings by individualizing dye process formulae to the facility's unique needs. The facility could also use this equipment to help optimize the use of chemicals such as acetic and formic acids, which are the two largest contributors to biological oxygen demand in the effluent.
Use of less expensive Chinese reactive dyes requires a two-step process that consumes more time, water, and energy than the one-step process that can be used with more expensive European dyes. The facility can conduct a detailed study of these two methods, comparing the cost of all inputs, not just the purchase price of the dye to determine which dye type best meets the facility's overall manufacturing goals.
The facility could install parallel bar screens in the jet room where drains meet and at the entrance to the main sewer sump to reduce the amount of total suspended solids and sedimentable solids from fabric lint in the facility's effluent. More efficient removal of lint would reduce the amount of organic material in the sump, thereby depriving bacteria of food. Sulfide and heat in the effluent also may be reduced by replacing the cover on the sump with a grate that allows light and air to enter. This would promote oxygenation, allow hydrogen sulfide to dissipate, and increase heat exchange, thereby cooling the effluent.
Three of the proposed changes could reduce steam consumption and lower fuel use, thereby reducing air emissions. Recapturing the heat from blowdown water is estimated to reduce fuel consumption by 2.4 percent or 19 metric tons of residual Number 5 oil per year.
Other proposed changes include recovering the heat in recycled bleach water and recovering the heat in recycled dye rinse waters, which could result in addition energy savings. Additionally, these changes will reduce emissions of carbon dioxide and heavy metals.
By undertaking both bleach and dye rinse recycling projects, the facility could reduce water consumption by up to 70,000 cubic meters per year. This also will reduce chemical use because bleach chemicals will be recovered for reuse. By using a dye process simulator, the facility could reduce the use and release of acetic acid, formic acid, and dyestuffs, major contributors to BOD levels in the facility's effluent.
For further information on this assessment or other activities sponsored by EP3, call the EP3 Clearinghouse at (703) 351-4004, send a fax to (703) 351-6166, or on Internet apendergathabaco.com.